Plate column



G. MARTIN Feb. 2, 1965 PLATE COLUMN .'5 Sheets-Sheet 1 Filed Jan. 18,1961 GAS TRAVEL |NvENToR GEORGES MARTIN ATTORNEY G. MARTIN Feb. 2, 1965PLATE COLUMN 3 Sheets-Sheet 2 Filed Jan. 18, 1961 INVENTOR MARTIN ATTORNFeb. 2, 1965 G. MARTIN 3,168,500

PLATE COLUMN Filed Jan. 18, 1961 s shee'slshee#v s INVENTOR GEORGESMARTIN BY www ATTORNEY United States Patent O 3,l3,6iii PLATE CLUENGeorges Martin, Sannois, France, assigner to Compagnie de SainbCfobain,Neniliyeuneinc, France Filed lan. i8, Eel, Ser. No. 83,455 Claimspriority, application France lieb. 3, 196@ 9 Claims. (ill. 261--i/l9)This invention relates to plate columns for eilecting con-` tact betweengasesand liquids. The column of the invention may be employed `forsimply the physical absorption of gas by the liquid, orimay be employedwith a process wherein the gas is absorbed in the liquid by reason of aVchemical reaction therewith.

The invention is particularly concerned with plate columns wherein theplates are provided with heat exchange coils in order to maintain theliquid on the plates at a temperature most favorable for a physicalabsorption or a chemical reaction. ln accordance with the invention, theheat exchange coils may either heat or cool the liquid.

The plate column of the invention may be employed, for example, in themanufacture of nitric acid. In one method of making nitric acid there isemployed one `or more plate columns in which oxides of nitrogen areabsorbed and oxidized by being passed through the column in thedirection from thexbottom to the top thereof in counter-current with aliquid which passes downwardly through the column from one plate toanother. The described absorption is exothermic; it is very importantthat the heat thus developed be progressively eliminated, be-

cause the absorption of NO2 in an aqueous liquid in the' lreoxidation ofN() toNOz arecarried out more eiliciently the lower the temperature.`

`Prior plate columns for carrying out the above process among othershave been provided with cooling coils so located as to lie within thelayer of liquid on the plates. Such cooling means have been most widelyused on the first plates of the column, that is, the plates at the lowerend thereof. In order to improve the cooling eillciency of Asuch coils,`the coils have `been disposed transversely with respect to th-e generaldirection in which the absorption liquid travels over the plate from thelocation of its admission to the plate to the location of its dischargefrom the plate ontothe next lower plate. ln order to improve theeillciency of heat exchange in such construction, baflles have beenplaced upon the upper surfaces of the plates, the battles being sodirected as to lie transversely to the general direction oftravel ofliquid on the plates. The described coils have been coiled around suchball'les.

No matter what the particular operation carried out in the column maybe, successive runs of the cooling coils must be placed close to eachother if a good eiliciency of heat exchange is to be obtained. Becauseof such close spacing of the tubes or pipes of the coils, there is leftlittle space for the circulation of liquid over the plates. Thus `thereis a large loss from the theoretical capacity of the column, the coolingcoils in effect constituting barriers to the ilow of liquidtherethrough; this causes a large variation-in the thickness of thelayer of liquid on the plates between the upper plates to which theliquid is iirst fed una A further object of the invention lies in theprovision of a plate column of the type indicated wherein at least someof the plates of the column are provided with heat exchange coils. p

Generally, the improvement in accordance with the invention consists` inthe provision of means for `guiding the absorption liquidron the platesinsuch mannerias to Vdisner, and so that after passing around the baillethe liquid is combined downstream of the baille in such manner that itcontacts substantially uniformly all the surface of the coil disposeddownstream of the baille. Y

In accordance with one preferred embodiment of the apparatus'of `theinvention, the plates are provided with a plurality of laterally spacedbales and with a` channel located upstream of the first baille `andperpendicularly to j the axis of such baille. Liquid introduced to theplate falls into the channel from which it spreads out laterally to llowalong the surface of the coil located upstream of the baille. Afterhaving passed out of contact with such upstream portion o't the coil,`the liquid passes inwardly along the downstream portion of the coilinto a second channel which is disposed as a prolongation of the iirstchannel.

' Fromthe `second channel the liquid starts a `second llow and thelowest plate from which the liquid is discharged from the column. Thepresence of the coils above the plates also causes heterogeneousdisturbances in the rate of travel of the gas through the platesprovided with the coils, thereby causing an additional loss inetliciency of `the column. Further, the liquid has a tendency to forceits way around the groups of tubes or pipes forming the coils, so thatthe rate of ilow of the liquid between the tubes in the main part of thecoils is small.

The present invention has as an object thereof the provision of animproved plate column for effecting Contact between a gas and a liquid.

cycle, this time passing along the portion of a second coil disposedupstream of a second bale, then around the ends ofthe second baille, andback to still a. further channel along the portion of the second coildownstream of the second baille.

The described'construction insures that the absorption liquid willcirculate past the entire cooling surfaces of the tubes which makeupthe'cooling coils. After having passed from one side of the plate to theother, bypassing around successive bailles as above described, theliquid is discharged from a plate so as to fall upon the next lowerplate.

In the drawings, forming a portion of the specication, there is shown anon-limiting preferred embodiment of a plate column in accordance withthe invention. The column is of the type useful in producing nitricacid, and has a plurality of multi-perforated plates located one abovethe other in spaced relationship in the column. Each plate carries ilvetransverse bailles and three sets of cooling coils, the coils beingdisposed respectively about the ilrst, third, and ilfth baille. In suchembodiment each group or set of cooling coils` is formed by twosuperimposed layers of pipes or tubes.

in the drawings:

FIG. 1 is a view in horizontal section through a column, the ligureshowing in plana plate provided with battles, heat exchange coils, andchannels in accordance with the invention;

FIG. 2 is a view in vertical cross section through the column and plateof FIG. l, the section being taken along the line 2-2 ofFlG. l; p

FIG. 3 is an enlarged View of the left hand portion of FIG. 2 taken online 2-2 of FIGel; l

FIG. 4 is a fragmentary view in elevation of the portion of theapparatus shown in FIG. 3, the view being taken in a direction fromright to left in FIG. 3;

FIG. 5 is a fragmentary view in horizontal section through the lett-handportion of the apparatus shown in 2, the section being taken along theline 5-5 of FIG. 2;

aisance lof FIG. 2.

In the drawings there is shown a portion of a vertical column having acylindrical side wall 4. Mounted 1n the column transversely thereof onbrackets 3a, 3b,

.aillxed to the wall there is shown a horizontal plate l which is madeup of an assembly of connected plate members. The resulting plate lextends completely across a section of the column and has an upstandingrim 4a extending around said plate and spaced from and parallel to sidewall 4. The main exent of the plate is provided with a plurality ofsmall openings 33 therethrough through which the gas rising in thecolumn may pass. The plate I is further secured to the column 4 bybraces in `the form of inverted channel members 2a, 2b, and 2c.

As particularly shown in FIGS. l and 2, the plate l is provided withfive parallel bafiles 5, 6, 7, 8, and 9. Each of the balles 5', 7, and 9is surrounded by its respective set of heat exchange coils formed by twosuperimposed layers of tubes lil and ll which are supported byconventional tube support means Ida. The two layers of tubes in eachcoil may be connected in series or parallel. The entering and exit endsof such tubes extend outwardly through the wall 4 ofthe column wherethey are connected to a suitable source and sump for heat exchangefluid. In the described preferred example of apparatus, for makingnitric acid, the coils are cooling coils and are connected to suitablecooling means such as a refrigerator compressor shown schematically at37 in FIG. 1.

Absorption liquid is fed to the plate l by two tubes 12 which lead froma similar plate disposed in the column above plate ll, such other plate(not shown) being r displaced at an angle of 180 with respect to plate labout the vertical axis of the column. The lower ends of tubes l2 leadto a distributor Ztl, 2l which will be described in more detail inconnection with FIGS. 3, 4, and 5. The discharge of liquid from plate lis eilected by two tubes i3, the upper ends of tubes i3 being connectedto a collector llo which will be described in detail in connection withFIGS. 6, 7, and 8.

The plate 1 is divided into three Zones A, B, and C by two spacedparallel partitions 6 and S. Such three Zones of the plate arerespectively provided with cross bailles 5, 7, :and 9 which are a1rangedsymmetrically thereto and parallel to partitions 6 and 8. The oppositeends of bailles 5, 7, and `9 are spaced substantially from the innersidewall of the enclosure 4 Iforming the column, such enclot sure, ineffect, forming a liquid-retaining rim about the plate 1. -Each zone ofthe plate is provided with a separate set of coiled heat exchange tubesIt), 11, such tubes being coiled about the respective bailles 5, 7, and9 in the rmanner shown in FIG. 1.

As will be seen in FIGS. 1 and 2, the liquid feeding means -`12 arelocated at zone A and communicate with a channel or trough 14 which isdisposed beneath the plate 1 between the feeding means 2i), 2J; and thebaille 5. The depth of channel 14 decreases in the direction from thefeeding means to the baille 5, becoming zero `adjacent the baille. Asseen in FIG. 1, the trough 14 has a width which is a smallparit of thewidth (diameter) of plate l. Downstream iof the baille `5 there is afurther channel 14a, the depth :of which increases progressively to amaximum at a location 15 beneath a partition 5. lFrom location 15 thedepth of channel 14a decreases progressively in the direction towardcentral baille 7, the depth of the channel decreasing to zero adjacentsuch baille. At lthe other side of baille 7 there lare .further channelsMb and 14C, channel l 14h being tthe same as channel 14a, and channel14C being the same as channel 14, except that it is turned with respectthereto. Channel llic discharges into a collector lo which is disposeddiametrically across the plate from the means `which feeds liquid to theplate.

It will be seen that the only path of communication between thesuccessive Zones A, B, and C of the plate is by way of the respectivechannels i461, lb'which pass beneath the partitions 6 and S. Thelocations of greatest depth of the channels lie beneath such partitions,so that the channels Imay accommodate all of the liquid flou/ulg betweenzones A, B, and C of the plate. The `channels are made of imperforatesheet metal, and aretconnccted at their open tops to slots in the bodyof plate l so that the upper edges of the sidewalls of the troughs lieflush with the upper surface of plate Il (FIGS. 2, 3, 4, 6, and 7).Ercept for the troughs, the horizontal plate l. is provided with aplurality of small holes 33 therethrough through which the gas rising inthe column may pass. The pressure yof such gas prevents any appreciableleakage of the liquid on the plate downwardly through holes 33.

YBy reference to FIGS. 1 and 2, it will be seen that the liquid feddownwardly through pipes 12 falls into trough 14 in which it ythen risesto ilow over the upper edges of the sidewalls 35 and 36 of such trough.As rnost clearly shown in FIG. 4, the upper edges :of such sidewalls 35and 36 lie ush with the upper surface of plate l. After rising ,to thelevel of the upper surface of plate l, the liquid in trough 14 spreadslaterally upon plate l in the rst zone thereof so as to ilow in eitherdirection along the straight portions of heat exchange tubes lil, llupstream of baille 5. The liquid then turns about the ends of baille 5and llows in two oppositely directed streams toward `the entering end oftrough 14th In so doing, the liquid generally follows the direction ofthe heat exchange tubes throughout the extent of the latter. As aboveset forth, the liquid passes from the Iilrst zone A to the second zone Bof plate 1 flowing beneath pantition 6 in trough 14a. Upon rising abovethe upper edges of the sidewalls of trough 14a the liquid enters thesecond end of zone B upstream of baille '7. It `will be obvious from theabove that liquid ilow conditions in both fthe second Zone B and thethird Zone'C of rplatevl are generally the same as those in the iirstzone, which have been described in detail. It will be :apparent that thedescribed ilow of liquid across zones A, B, and C yfrom the entering endof channel 14 to the exit end of channel 14e takes place by reason ofthe lfact that the liquid level :at zone A is `at least slightly greaterthan that at lzone B, and that the liquid level at zone B is at leastslightly greater than that at zone C. g

Turning now to FIGS. 3, 4, and 5, the details of thel means `for feedingabsorption liquid onto the .plate 1 will now be described. The means `onthe plate fed by tubes 12`v is essentially in the `form of a tank 2li,tank y20 being generally oblong in shape and straddling the trough 14'symmetrically with respect to the center line X-X thereof. One tube 12is disposed with its lower end in one end of tank Ztl at one side oftrough 14 and the other rtube 12 is symmetrically disposed at the otherend of tank 29. Tank 2@ is divided into three compartments by twoparallel partitions 21, 21a which extend from the bottom of tank 2ligenerally intermediate the height of the tank. As shown, partitions 2l,2M are parallel and spaced apart a distance equal to lthe width oftrough I4. There are ithus formed two compartments 22 and 22a located atthe i ends of tank 2li. The lower ends of the respective pipes `l2extend into compartments 22 and 22a to a depth appreciably below theupper edges of partitions 21 and 21a. The bottoms of compartments `22,22a are imperforate so that the liquid fed thereinto by the pipes 12must rise above the upper edges of partitions 21, 21a before it can iiowdownwardly into trough 14.

In FIGS. 6, 7, and 8 the means for discharging liquid from plate l isshown in detail. An oblong open-bottomed tank 3d, generally similar tothe above-described tank 20,v

encased straddles the trough `1de symmetrically with respect to thecenter line Y-Y thereof, Liquid traveling in trough 14C passes upwardlyover the upper edges 35C and 36C 0f trough `1de and rises into thecentral portion of tank 30 and vents into the upwardly flared ends 3-1,32 of collector tubes v13. The upper edges oi members 31 and 32constitute seals or partitions over which the liquid in tank 30 mustflow before the liquid `tlows downwardly in the tubes yllr. The tubes113 lead to the next lower plate in the column which may be of the sameconstruction `and be fed with liquid in the same manner as the plate d.

The construction of the plate in accordance with the invention improvesto a considerable extent the exchange of heat between the liquid on theplate and the heat exchange tubes 10, l11. At 'the same time, theconstruction in accordance fwith the invention oltsets the loss ofcapacity of liquid caused by the .presence of the heat exchange coils.The construction also permits the size of the column to be reduced whilemaintaining the same production; alternatively, all :other things beingequal, a column in accordance with the invention has an increasedproductive capacity over a conventional column of the same size. Theconstruction of the invention eliminates diiiculties encountered inprior columns due to non-uniformity in spacing of the heat exchangetubes on the plates.

.T he apparatus is of particular advantage when employed in absorptioncolumns for oxides of nitrogen in the making of nitric acid. In suchprocess the eihciency of .cooling of `the liquid on the plates by thecooling coils has a large effect upon the commercial success of theprocess.

When the column in Awhich the plates of the invention are used is Voflarge diameter, on the order fof four meters or more, the plates must besupported by large strong framework in the column. Such framework isadvantageously located beneath the badles 5, '7, and 9. Theabovedescribed bracing members 2a., 2b, and i12-c indicate one manner inwhich :the plates may be thus additionally supported. Such manner ofadditional support of the plates leaves the tops thereof unencumberedand does not interlfere with a circulation of the liquid throughout thezones thereof or between successive zones.

In cases in which contact between the gas and the liquid gives rise toappreciable frothing of the liquid, the partitions, such as those shownat `t and S, dividing the plate into successive zones may be totally orpartially interrupted, as above the `froths, to permit the free passageof the froth.

Although only one embodiment of the invention has been illustrated inthe accompanying drawings and described in the foregoing specication, itis to be especially understood that various changes, such las in therelative dimensions of the parts, materials used, and the like, as well.as the `suggested manner of use of the apparatus of the invention, maybe made therein without department from the spirit and scope of theinvention as will now be apparent to those skilled in the art.

What is .claimed is:

1. In apparatus having 1a horizontal plate multiperorated over its mainextent and adapted to retain a substantial depth of liquid thereon asthe liquid travels generally across the plate, means forming a liquidretaining rim about the plate, the improved plate which comprises meansfor introducing liquid to the plate at a iirst location in a zone of theplate, means for discharging liquid from the said zone ofthe plate at asecond Vlocation in said zone, the iirst and second locations beingsubstantially spaced from eachother along the direction of general tlowof 'the liquid across the plate, an upstanding bai-lie on the plateextending generally transversely of such direction of general travel andbetween the first and second locations, the battle spanning asubstantial portion of the width of said Zone but having its ends spacedsubstantial distances from the edges of the plate, a heat exchange tubecoiled around the baille so as to lie generally within the liquid onsaid zone of the plate, the turns of the tube being disposed so as to beV.trough parts, said :firs-t trough part extending from the liquidfeeding means to the baille and having a depth which decreases from theliquid feeding means to the baffle, and

said second trough part extending from the bafe to the liquiddischarging means and having a depth which increases from the bathe tothe liquid discharging means, said trough causing the liquid deliveredto the inlet end of the trough by the feeding means Ito spread out anddow laterally on the upstream side of the baffle `gen-erally parallelthereto and causing the liquid, after it has liowed around the endsofthe baffle and inwardly on the downstream side ofthe baflle, to berecombined in the exit end .of the trough before owing into thedischarge means.

2. An apparatus as dened in claim 1, wherein each trough part has awidth which is a small part of the Width of the plate, said trough partsbeing disposed below the plate, and the open upper end of each troughpart directly communicating with the upper surface of the plate.

3. An apparatus as defined in claim 2, wherein the upper ends of thetrough parts lie generally at the level of the upper surface of theplate.

4. An apparatus as defined in claim 1, wherein the plate is divided intoa plurality of isolated zones by at least one partition member extendingacross the plate from each edge to the other and generally parallel tothe first recited battle, each such zone being provided with a baflie, aheat exchange tube coiled around its respective bathe, a third troughpart aligned with said first and second trough parts and extending fromthe bafe in one zone to the baille in the adjacent zone and having adepth which increases from the bafe in said one zone to a point inalignment with said partition and then decreases to the Ibathe in saidadjacent zone whereby said third trough part furnishes the only means offlow of liquid between adjacent zones on the plate.

5. ln a plate column adapted to effect contact between a gas and aliquid, said column having an upstanding enclosure with a plurality ofvertically spaced horizontal plates therewithin spanning the enclosure,said plates being multi-perforated over their main extents and a rimabout the plate to retain a Vlayer of liquid thereon as the liquidtravels generally across the plates, the improved plate which comprisesmeans for introducing liquid to the plate at a rst location in a zone ofthe plate, means for discharging liquid from the said zone of the plateat a second location in `said zone, the rst and second loca tions beingsubstantially spaced from each other along the direction of general llowof the liquid across the plate, an upstanding battle on the plateextending generally transversely of such direction of general travel andbetween the first and second locations, the bathe spanning a substantialportion of the width of said zone but having .its ends spacedsubstantial distances from the edges of the plate, a heat exchange tubecoiied around the bafe so as to lie generally within the liquid on saidzone of the plate, the turns of the tube being disposed so as to begenerally distributed over said zone of the plate, the portions of thecoil both upstream and downstream of the baie lying generally parallelto each other and to `the broad extent of the bafc, liquid channelingmeans lying generally along the direction from the feeding means to thedischarge means, the channeling means comprising a trough having firstand second parts disposed generally normal to the bathe, opening meansextending through said plate and overlying the length of said first andsecond trough parts, said first trough part extending from the liquidfeeding means to the bale and having a depth which decreases from theliquid feeding means to the baille, and said second trough partextending from the baille to the liquid discharge means and having adepth which increases from the baille to the liquid discharging means,said channeling means causing the liquid delivered by the feeding meansto the inlet end of the trough to spread out and flow laterally on theupstream side of the baille generally parallel thereto and causing theliquid, after it has flowed around the ends of the baille and inwardlyon the downstream side of the baiile, to be recombined in the exit endof the trough before flowing into the discharge means.

6. An apparatus as dened in claim 5, wherein each of the trough partshas a Width which is a small part of the width of the plate, said troughparts being all of subystantially the same width, said trough partsbeing disposed below the plate, the upper end of each of the trough partdirectly communicating with the upper surface of `the plate.

7. An apparatus as defined in claim 6, wherein the upper end of each ofthe trough parts lies generally at the level of the upper surface of theplate.

8. A plate column as defined in claim 5, wherein the plate is dividedinto a plurality of isolated zones by at least one partition memberextending across the plate from each edge to the other and generallyparallel to the first recited baiile, each such zone being provided witha baie, a heat exchange tube coiled around its respective baille, athird trough part aligned with said iirst and second trough parts andextending from the baffle in one zone to the baffle in the adjacent Zoneand having a depth which increases from the baille in said one zone to apoint in alignment with said partition and then decreases to the bailiein said adjacent zone whereby said third `trough part furnishes the onlymeans of flow of liquid between adjacent Zones on the plate.

9. A plate column as deiined in claim 5, wherein the means fordischarging liquid from the plate includes a tank straddling the lasttrough part in the plate, the tank having at least one collectorcompartment therein, the collector compartment having a partition overwhich liquid ilows into the compartment, and conduit means leading fromthe lower end of the collector compartment to the feeding means for thenext lower plate in the column.

References Cited in the iile of this patent UNITED STATES PATENTS1,328,259 Barbet Jan. 20, 1920 2,290,209 Rosenthal July 21, 1942 FOREIGNPATENTS 151,988 Great Britain Dec. 1, 1921 630,884 Great Britain Oct.24, 1949 737,315 France Oct. 3, 1932 803,212 Great Britain Oot. 22, 1958

1. IN APPARATUS HAVING A HORIZONTAL PLATE MULTI-PERFORATED OVER ITS MAINEXTENT AND ADAPTED TO RETAIN A SUBSTANTIAL DEPTH OF LIQUID THEREON ASTHE LIQUID TRAVELS GENERALLY ACROSS THE PLATE, MEANS FORMING A LIQUIDRETAINING RIM ABOUT THE PLATE, THE IMPROVED PLATE WHICH COMPRISES MEANSFOR INTRODUCING LIQUID TO THE PLATE AT A FIRST LOCATION IN A ZONE OF THEPLATE, MEANS FOR DISCHARGING LIQUID FROM THE SAID ZONE OF THE PLATE AT ASECOND LOCATION IN SAID ZONE, THE FIRST AND SECOND LOCATIONS BEINGSUBSTANTIALLY SPACED FROM EACH OTHER ALONG THE DIRECTION OF GENERAL FLOWOF THE LIQUID ACROSS THE PLATE, AN UPSTANDING BAFFLE ON THE PLATEEXTENDING GENERALLY TRANSVERSELY OF SUCH DIRECTION OF GENERAL TRAVEL ANDBETWEEN THE FIRST AND SECOND LOCATIONS, THE BAFFLE SPANNING ASUBSTANTIAL PORTION OF THE WIDTH OF SAID ZONE BUT HAVING ITS ENDS SPACEDSUBSTANTIAL DISTANCES FROM THE EDGES OF THE PLATE, A HEAT EXCHANGE TUBECOILED AROUND THE BAFFLE SO AS TO LIE GENERALLY WITHIN THE LIQUID ONSAID ZONE OF THE PLATE, THE TURNS OF THE TUBE BEING DISPOSED SO AS TO BEGENERALLY DISTRIBUTED OVER SAID ZONE OF THE PLATE, THE PORTIONS OF THECOIL BOTH UPSTREAM AND DOWNSTREAM OF THE BAFFLE LYING GENERALLY PARALLELTO EACH OTHER AND TO THE